I don't think that cards from the commander decks that are not in the main set are standaard legal. Scryfall.com has It marked as not legal. You can check by searching cards on that site.
Most of the hydra's are not standard legal as wel. If you use the Advanced Search methode you can search for all hydra's that are legal in standard. Maybe you can make it an Explorer or Historic deck.
And for a +1/+1 counter deck in standard you can look at Simic for all kinds of proliferate and
ozolith, the shattered spire. I have one andit'sgood enough for reaching gold on the ladder in Arena (bo1).